Virtualization may be used to provide some physical components as logical objects in order to allow running various software modules, for example, multiple operating systems, concurrently and in isolation from other software modules, on one or more interconnected physical computer systems. Virtualization allows, for example, consolidating multiple physical servers into one physical server running multiple virtual machines, which may increase the hardware utilization rate.
Virtualization may be achieved by running a software layer, often referred to as a hypervisor, above the hardware and below the virtual machines. A hypervisor may run directly on the server hardware without an operating system beneath it or as an application running on a traditional operating system. A hypervisor may virtualize the physical layer and provide interfaces between the underlying hardware and virtual machines. Processor virtualization may be implemented by the hypervisor scheduling time slots on one or more physical processors for a virtual machine, rather than a virtual machine actually having a dedicated physical processor. An input output memory management unit (IOMMU) may also be virtualized. An emulated or virtual IOMMU may be used to limit access of specific devices (e.g., virtual devices). Using the virtual IOMMU, a guest of virtual machines may grant access to a virtual device and/or later revoke that access.